The invention relates to a method of producing a series of images for display on a display device and to a display device which is arranged to display such a series of images. A particular, but not exclusive, application of the invention is in a television receiver.
A method and apparatus for transitioning between sequences of images is disclosed in U.S. Pat. No. 5,353,391. This patent discloses a method and apparatus for generating and viewing a transition between a first and second sequence of images on a computer controlled display system. The method of the invention involves several steps, including: providing a first and second sequence of digitized images, which are typically stored in the computer system; providing the duration of total time of the transition between the first and second sequence of images; providing a resource means for specifying the transition between the first and second sequence; determining a first portion of the first sequence of images (the first portion having a duration in time less than or equal to the duration of the transition); determining a second portion of the second sequence (the second portion of the second sequence of images having a duration in time less than or equal to the duration of the transition); creating a transition template from the transition resource, the transition template having a duration equal to the transition; and combining the first portion of the first sequence and the second portion of the second sequence with the transition template to thereby produce a third sequence of images. The step of creating a transition template from the transition resource is further comprised of the steps of selecting objects, interpolating objects and/or a source image area and mapping objects to a source image area. In the combining step, the transition template is used to determine which portions of the first source sequence, the second source sequence, or both will be displayed in the third sequence of images. Also provided is a means for modifying a duration of the entire transition or for modifying a duration of individual frames within the transition.
This method and apparatus involves the use of a personal computer which includes extensive memory and a relatively expensive microprocessor.
Television receivers are known which use a microprocessor to control the operation of the various circuits of the receiver and which produce on screen displays to enable the user to access various features. Such receivers may also include data capture circuits which are used to obtain services such as teletext which displays broadcast text messages on the screen. Such receivers will have a character generator which contains a plurality of sets of characters in the form of bit maps of a particular character. Thus each character may for example occupy an array of 16xc3x9712 pixels. The teletext data as transmitted will address particular characters in the character generator to cause them to be displayed on the screen at the appropriate location. These character sets can also be used for on screen display under the control of the microprocessor. It is sometimes desired to have special characters which do not form part of one of the standard character sets that are stored in the character generator. These special characters may be stored in memory associated with the microprocessor or may be generated by the microprocessor itself and are known as dynamically redefinable characters in that the microprocessor can redefine these characters during a sequence of steps. Thus the character generator may include a portion of random access memory into which the microprocessor may write these redefinable characters. These characters may then be displayed on the screen using the normal processes of the character generator.
It is an object of the invention to enable the provision of a method of producing a series of images for display on a display device using an inexpensive micro processor such as a typical television microprocessor and using quantities of memory which are associated with consumer apparatus. That is to enable the use of a comparatively inexpensive microprocessor and a relatively small amount of memory.
The invention provides a method of producing a series of images for display on a display device using a microprocessor having a non-volatile memory and a display RAM comprising the steps of:-
a) providing each image in the form of a bit map,
b) resolving each of the bit mapped images into an nxc3x97m array of dynamically redefinable characters (DRC) of axc3x97b pixels, where a, b, m, and n are integers,
c) storing each of the DRCs forming each of the images in the non volatile memory,
d) copying under the control of the microprocessor the array of DRCs for each image in turn from the non volatile memory into a display RAM to create a bit mapped image, and
e) displaying in turn each of the bit mapped images.
The method according to the invention depends on the realisation that if there is a possibility of having dynamically redefinable characters displayed on a screen and that there are enough of these characters to form an array into which an image may be inserted, then this enables the user of a comparatively inexpensive microprocessor to select the dynamically redefinable characters for display and to write them into a display RAM to create what is effectively a bit map image made up of an array of dynamically redefinable characters. Thus if a sequence of such images is stored in the form of a sequence of arrays of dynamically redefinable characters in a non-volatile or a read only memory the microprocessor can collect these arrays of redefinable characters and transfer them at the appropriate time to the display memory to enable a sequence of images to be displayed. The process of converting the images in the form of bit maps to an array of dynamically redefinable characters is not carried out by the microprocessor in the display device but is rather carried out using a personal computer or work station to create data files which consist of the dynamically redefinable characters for each image. These are then written into the non volatile memory either at the time of manufacture in the case of a read only memory or in the case of a non volatile read/write memory may be entered into the memory at a later date. It is possible that such images could be transmitted via a teletext channel when the display device forms part of a television receiver if a read/write non-volatile memory was provided. Thus any data channel which transmits data which can be captured by a data capture circuit within the television receiver could transfer such sequence of images into the non-volatile memory.
DRCs that are unchanged between successive images may be stored only once in the non-volatile memory. Thus it is not necessary to store the whole of each of the successive images but instead only those DRCs which contain changed information need to be stored. This gives a reduction in the size of the non volatile memory required to store most sequences.
Each image may be contained in an array of up to twenty five dynamically redefinable characters. This number is not an absolute limit, but represents a reasonable allocation of display memory for a consumer device. It would of course be possible to provide larger arrays for a higher end television receiver which offers a greater number of features and commands a premium price which can justify the cost of additional memory.
A first image may be transformed to a second image by gradually distorting the first image so as to move chosen points on the first image to the position of corresponding points on the second image. Such a process has been referred to by the term xe2x80x9cmorphingxe2x80x9dand may be used to dissolve one image into another.
The method may comprise the steps of:
f) creating a first list of positions of pixels of a given colour in the first image,
g) creating a second list of positions of pixels of the given colour in the second image,
h) mapping each pixel in the first list to its closest partner in the second list,
i) mapping each remaining pixel in the second list to its closest partner in the first list,
j) calculating the position of each pixel in intermediate images between the first and second images to create intermediate lists of positions of pixels,
k) converting each of the lists created in step j) into a bitmap image,
l) resolving each of the images produced in step k) into an array of DRCs,
m) storing the DRCs of each image in the non-volatile memory, and
n) carrying out steps d) and e).
This procedure would normally be carried out using a personal computer or work station to generate a data file of successive images which can then be copied to the non-volatile memory of the television receiver. This could be at the time of manufacture as with a mask programmed read only memory formed on the same chip as the microprocessor or could be in additional memory which could be replaceable or re-programmable to enable new sequences to be produced either instead of or in addition to the original sequences.
Steps c) and d) may be carried out using Pythagoras"" theorem to calculate the positions in the x and y dimensions. Step e) may be carried out by dividing the change in x and y directions by the number of intervening images to produce the intermediate positions for each pixel. Thus if for example there are eight intervening frames between the first image and the second image the distance between the pixels in the first and second images is divided by eight to produce the intermediate positions in each of the intervening frames.
The invention further provides a display device comprising a microprocessor having a non-volatile memory associated therewith, a display arrangement for displaying on screen display text and/or graphics generated by said microprocessor, said display arrangement including a memory for storing a standard set or sets of characters, a portion of memory for storing dynamically redefinable characters (DRCs), and means for displaying selected characters from said standard set or sets or from said DRCs, wherein the non-volatile memory contains a series of images each of which is resolved into an array of DRCs, and the microprocessor is arranged to transfer each of the images in turn into said portion of memory in the display arrangement in order to display a selected sequence of images.
Such a display device is arranged to carry out the method of the invention and is capable of displaying animated images or of morphing between two images. This has particular application in television receivers incorporating such a display device and gives an enhanced on screen display capability enabling manufacturers to provide more attractive on screen displays for their products, perhaps involving cartoon characters or other logos having given animation effects and of providing an attractive transition from one title to another. Thus by using this technique a television manufacturer can differentiate its products from those of other manufacturers.